The present invention relates to papermaking machines, and more particularly relates to a method in a papermaking machine for switching the winding of a paper web from a fully wound roll onto a new empty reel shaft to start a new paper roll.
Production speed of tissue web is of paramount importance. Production speeds for tissue webs have leveled off in recent years. This is thought to be a result of the increasing demand for high-quality tissue and the technical difficulty of maintaining higher production speeds. At higher production speeds the tissue webs tend to vibrate and rupture due to their low basis weight and tensile strength.
Reel changing comprises switching a completed paper roll with a new, empty reel shaft and initiating tissue web winding on the new reel shaft. Efficient reel changing increases overall production speed by minimizing the length of downtime between reels and the number of failed reeling attempts.
A common way to initiate tissue web winding on a new reel is by threading. Threading means that a web end is pulled along through a paper or board machine by a leader. The leader consists of a strip of web which may initially be only 40 to 50 cm wide, but gradually becomes wider until it extends across the entire width of the web. The leader is cut out in the continuous web, starting either at one edge or somewhere at an optional distance from either edge of the web, whereas its length is determined by the time it takes for the tip to extend across the entire width of the web. Due to the high web speed the leader may be very long, 180 to 200 m. This incurs considerable costs for the paper mill since the cut part of the paper web must be discarded for each paper reel.
Sanitary tissue products, usually manufactured of tissue paper, are extremely market-sensitive and the quality of the product is therefore often more important than its quantity. It is thus important that during reeling the paper reel acquires several important properties, e.g., homogeneity and lack of wrinkles, tears or folds. Furthermore, high efficiency in the following conversion machines can only be achieved if the reels of paper from the paper machine have a homogenous high quality.
Soft paper with low strength must be reeled carefully in order to keep the paper qualities such as density and elasticity as constant as possible throughout the reel. The two main factors affecting reel density are web tension and radial pressure at the nip of the reel-up. Lower nip pressure is important to obtain lower average density.
The thickness and elasticity of the web decreases from the outside of the reel to the center in a radial direction. This is because the compressive stress is built up in the paper reel during reeling and compresses the inner radial parts of the reel. This causes a decrease in thickness of the inner web layers. This effect increases if the reel is stored for too long before being rewound or converted.
Reeling problems arise when a new reel of paper is commenced with the aid of the tapered leader as mentioned above, since the web turns applied during winding of the innermost layers produce an uneven radial growth axially along the reel shaft so that the reel becomes carrot shaped. This is caused partly by the superelevation of the web and partly by differences in the nip pressure across the web. If the cross-sectional profile of the paper web differs with regard to thickness, web tension or elasticity then pleating, crushing damage, defects in web and axial forces in the reel will occur at a high nip pressure. This may, in worst cases, result in web rupture.
High web speed machines use either the threaded or full-width methods and must wrap the web around the empty reel shaft. Changing xe2x80x9cfull-widthxe2x80x9d reels in the present context refers to wrapping the entire width of the web around the reel shaft when initiating a new reeling operation. This is to be distinguished from threading using a tapered leader. At high web speeds, glue is applied to the leader itself before it is threaded. At low speeds, such as those used for tissue paper production, full-width methods assisted by balloon blowing are common. Balloon blowing entails creating slack across the full width of the web by somewhat retarding the rotation of the finished reel. With the aid of compressed air, the fold thus formed is then forced into the nip between the new reel shaft and the reel drum, after which the web is cut off. In order to increase the reliability of this type of reel switching, glue or tape is also applied, but only on the actual reel shaft before this comes into contact with the paper web.
Many methods of glue or adhesive application have been used such as manual application using a large brush or spray gun as shown in FIG. 10. Regardless of the transfer method used for switching reels, it is important that the glue is still adhesive when contact occurs between the paper web and reel shaft. It is thus desirable to use simultaneous glue spraying as opposed to manual methods. A range of conventional glue types have been used to ensure that the paper web adheres to the reel shaft.
Automatic glue spraying is accomplished with the aid of glue nozzles, generally placed at one side of the paper web, close to the primary arms. U.S. Pat. No. 6,045,085 demonstrates the use of aerosol jets for glue application. This invention mixes compressed air of predetermined amounts with the conventional liquid glue or adhesive as it exits a nozzle. The nozzle is actually one nozzle inside another, one of which sprays the compressed air and the other the liquid glue. The glue is distributed in a flat and wide fish tail pattern by several of the nozzles arranged side-by-side on a screen mounted upstream of the paper reel.
Despite the increases in speed of glue application using aerosol jets, and other automatic gluing methods, a problem remains as to the best manner for severing the existing continuous web from a completed roll. One automatic method that has been used for severing a web employs the use of water jets, or other cutting devices, sprayed at a high velocity to rupture the paper web. It is desirable to eliminate these water jets or other cutting devices.
Therefore, it would be advantageous to have a method of automatically applying glue, severing a paper web and ensuring the integrity of the glued interface to facilitate a quick and effective reel change in a papermaking machine.
The current invention meets these and other needs by providing a method for winding a traveling web of paper in which the paper web is guided toward a rotating reel shaft using a web supporting surface, such as a reel drum. An adhesive is sprayed from a spray nozzle onto at least one of the web and the reel shaft. Contact is initiated between the web and the reel shaft such that the web adheres to the reel shaft, and forms an adhesive interface that follows being winded on the reel shaft therebetween. A trailing end extends from the adhesive interface in a downstream direction while a leading end of the web extends from the adhesive interface in the upstream direction. The web is then severed at the adhesive interface by applying tension to the trailing end of the web in the downstream direction, the adhesive preventing the web from detaching from the reel shaft such that the trailing end of the web tears free of the leading end.
The adhesive is preferably heated to a predetermined temperature in a tank with a heater to render the adhesive flowable and the adhesive is then supplied to the spray nozzle. Other types of high tack (i.e., thick and sticky) adhesives may also be employed in the severing process. A second nozzle can be added for spraying the adhesive in alternative patterns such that the tear line of the web has various shapes. In a first embodiment, the first and second nozzles are positioned at the edges of the web and translated to the center of the web while spraying adhesive such that the web tears along an adhesive interface extending diagonally from the edges to the center of the web in the upstream direction. In a second embodiment, the first and second nozzles begin at the center of the web and are translated to the opposing edges of the width such that the web tears along an adhesive interface extending diagonally from the center to the edges of the web in an upstream direction. Alternatively, a plurality of fixed nozzles with overlapping spray jets can be used to spray adhesive simultaneously across the web width such that the web tears across the full width of the web.